The present invention relates to a pointer resetting mechanism for a magnet disc operated gauge mainly adapted for use in vehicles. Such a pointer resetting mechanism is made up of a coil spring particularly housed together with a floatable magnet disc for protection in a sealed shelter case and at least an auxiliary magnet received in one of a tubular columns in a lower case of the shelter case. The spring has one end fixed to a pointer shaft and the other end secured to a retaining means disposed on the case. Around the sealed shelter case is wrapped around induction copper wires. When an electric current appears in the copper wires, the magnet disc floating in damping oil is forced by induced magnetism to rotate in the shelter case and when the electric current is removed the pointer can be automatically reset by way of the mechanical biasing force of the coil spring. Furthermore, the auxiliary magnet is used to make the pointer operate more stable at its initial position at where the coil spring can not produce enough tension to firmly hold the pointer in position. When the pointer is moved within or over a half circle range, the coil spring is extended in such a manner that it will produce larger tension to hold the pointer, the auxiliary magnet can constantly help the pointer to overcome the tension by attracting the magnet disc to spin clockwisely. When the pointer moves back to its initial position, the auxiliary magnet can also exert force on the magnet disc so as to help the pointer move smoothly backwards.
Moreover, the sealed shelter case is full of damping oil in which the coil spring as well as the magnet disc is totally immersed The damping oil in the shelter case of a conventional gauge easily leaks out when a pointer shaft with a magnet disc spun in the damping oil back and forth for a long period of time as a result of pressure built up in a specific area. In the present invention, the coil spring is housed inside the shelter case and mounted onto a pointer shaft under protection and the coil spring having a plurality of concentric rings can effectively hold damping oil therein so that pressure built in the shelter case can be evenly distributed in practical operation without causing leakage in the shelter case.
There are a number of prior art pointer resetting means developed in these years which can make a pointer automatically resume to a starting position. However, they still have some disadvantages in consideration of structure and cost in production and maintenance.
Referring to FIGS. 1, 1A, the first prior art pointer resetting mechanism adopts a coil spring 6A secured to a front portion of a shaft 21A onto which a pointer 4A is mounted. Thereby the pointer 4A can be automatically reset to its initial position when a gauge stops functioning in operation. As further shown in FIG. 1A, the magnet disc 20A and the damping oil 30A are housed in a shelter case made up of an upper case 10A and a lower case 11A with the shaft 21A integrally secured to the magnet disc 20A. The coil spring 6A is fixed to the exposed front end, as shown in FIG. 1 so as to permit the shaft 21A to be retractably operated. Such a prior pointer resetting mechanism exposes the delicate coil spring 6A externally without any protection, it can be easily deformed or damaged in the process of assembly and maintenance.
As shown in FIG. 2, the second prior art is a gauge equipped with a coil operated pointer 4B wherein the magnetism producing coil 5B is movably mounted onto and operated along a C-shaped laminate 8B of plates which are subject to a strong magnetism produced by a magnet block 9B and a very light and fragile pointer 4B is secured to the coil 5B so that when an electric current is present in the magnetism producing coil 5B, the pointer 4B is able to give indication to marked numerals on a face board 7B for measurement of a certain functional property, such as pressure, speed and etc. Such a prior pointer system enables a pointer to be automatically reset by a tiny coil spring (not shown) fixed in front of the movable coil on the shaft as long as the electric current in the coil disappears. However, this gauge is extremely sensitive to vibration and the pointer is very light and delicate and is vulnerable to any external shock, vibration and impact. This prior gauge system with an automatic resetting pointer is not satisfactorily accepted as a result of its bulky size and vulnerability to damage.
In a third prior pointer resetting mechanism, a gear assembly is used. Such a gear assembly is complicated in structure, relatively bulky in size and expensive in cost, causing such a king of gauge to be less competitive in markets and harder for maintenance.
In a fourth prior pointer resetting mechanism, a step motor is mounted in a gauge so as to enable a pointer to reset to an initial position automatically. This kind of resetting mechanism is very expensive due to the high cost of a step motor which is delicate in structure and is easily out of function as a result of shock or collision. This type of pointer resetting mechanism is too expensive to be competitive in markets. So, such a prior art can not be widely accepted by consumers at all.